1. Technical Field of the Invention
The present invention relates to an exchange such as PBX (Private Branch Exchange) composed to allow to conveniently execute emergency call such as Enhanced 911 call.
2. Related Art
FIG.17 shows a system for emergency call composed using PBX 10. In this system, an E911 unit 4 to be connected to a CAMA (Centralized Automatic Message Accounting) line 7, one of corresponding lines for realizing an Enhanced 911 call (called E911 call, hereinafter), is connected to the outside of the PBX 10, to be used as adapter of the PBX 10 and the CAMA line 7.
Here, an E911 call is an emergency call (911 call) of which function is enhanced. According to this E911 call, it is adopted an approach wherein caller ID information or the like are sent to a station upon originating of an emergency call and the station obtains the caller location information based on this information, apprising facilities for emergency, where fire-fighting or similar emergency team is watching, of this information. As a consequence, the emergency team can arrive at the origin of call without fail.
The E911 unit 4 is an interface for transmitting the caller ID or others via the CANA line 7 and is provided with a procedure for sending the caller ID (IF tone signal) to the station via T1 (digital) or TIE (bus) line or the like.
To the PBX 10 of FIG. 17 are connected an digital key telephone 2 and a standard telephone set 3 and, on the other hand, it is connected to the E911 unit 4 via a general purpose bus 6 such as TIE line, and is connected to the public network (PSTN) 5 via respective lines. The 911 unit 4 is connected to a 911 Tandem Office 8 via the CAMA line 7.
Moreover, the PBX10 comprises a control section 11 including a time switch 111, a transmitting and receiving interface 12, a digital line interface 13, a DKT (digital key telephone) interface 14, a standard telephone set interface 15, and a station line interface 16, the control section 11 and respective interfaces 12 to 16 being connected by a PCM highway (speech highway) L1 and a data highway L2.
In addition, the E911 unit 4 is composed as shown in FIG. 18.
The E911 unit 4 includes a receipt detector 61 for detecting a call-in from the PBX 10, a dial detector 62 for detecting dial data of DTMF signal originated from the PBX 10, a CPU 63 for supervising and controlling operations of the E911 unit 4 and a CAMA line interface 64 to be connected to the CAMA LINE 7. Plural elements other than the CPU 63 are provided with so as to allow simultaneously a plurality of E911 calls from the PBX 10.
Upon arrival of a call-in signal from the PBX 10, the call-in detector 61 detects it and inform the CPU 63 of receipt detection. Now, the CPU 64 waits that an extension number allocated to an extension telephone terminal sent by the PBX 10 be detected by the dial detector 62. This extension number serves as an ANI (Automatic Numbering Identification) signal corresponding to the caller location information. Upon the detection of the transmitted extension number by the dial detector 62, the CAMA line interface 64 closes the CAMA line 7, sends a connect signal to 911 Tandem Office 8 and, moreover, transmits the extension number (ANI) detected. Owing to this, the 911 Tandem Office 8 obtains the caller location information based on this information and apprises facilities for emergency, where fire-fighting or similar emergency team is attending, of this information. At the same time, the PBX 10 will be connected to the CAMA line 7 via the call-in detector 61 and the CAMA line interface 64, enabling the emergency call.
The emergency call operation by the PBX 10 mentioned above will be described in reference to the flow chart of FIG. 19. Upon a dial input (S501) via the DKT interface 14 from the digital key telephone 2, the control section 11 of the PBX 10 determines whether it is an E911 call or not (S502). In other words, if "911" is dial-input, it constitutes an E911 call, originating the step S503 to capture a trunk leading to the E911 unit 4 through the digital line interface 13 (S503).
At that time, the control section 11 determines whether there is or not a vacancy in the CANA line interface 64 inside the E911 unit 4 (S504), and if there exists the vacancy, calls in the E911 unit 4 and then change an ANI signal including ID information of the digital key telephone 2 into a DTMF signal and transmits the DTMF signal to the E911 unit 4 via the general purpose bus 6 for performing an E991 call (S505).
Here, the ANI corresponding to the caller location information is registered in the control section 11 of the PBX 10 in response to the extension telephone. The E911 unit 4 receives the ANI signal transmitted from the PBX 10, converts it into MF tone signal and sends it to the 911 Tandem Office 8 through the CANA line 7. The 911 Tandem Office 8 has the composition for retrieving the database of caller location information ALI (Automatic Location Information) corresponding to the ANI signal and for delivering, from this information, an emergency message communication to a firehouse or the like nearest to the caller. Therefore, it can advantageously transmit surely and rapidly where an emergency message has been generated, without calling a PSAP (Public Safety Answering Point).
In the step S502 of FIG. 19, if it is determined that it is not an E911 call, a call processing using the public network (PSTN) 5 shall be performed by the station interface 16 (S506). On the other hand, in the step S504, if there is no vacancy in the CAMA circuit interface 64, an ordinary emergency call processing to call the nearest firehouse or the like using the public network 5 by the station line interface 16 shall be performed (S507).
As mentioned above, when an E911 call is to be made from the PBX 10 using the E911 unit 4, if the CAMA circuit interface 64 in the E911 unit 4 is occupied, the E911 call can not be made, even if there exists an interface (such as transmitting and receiving interface 12) connected to an E911 call corresponding line by MF signal, because the PBX 10 is lacking for MF signal source though it includes a mechanism for transmitting a DTMF signal. To resolve this inconvenience, it has been necessary to dispose an MF signal source in the PBX 10.
FIG. 20 shows a block diagram of the control section 11 provided with a MF signal source. In this example, an MF tone generation circuit 114 for generating more various MF tones than the dial key corresponding DTMF tone is added to the control section 11 in the PBX 10, in addition to a DTMF tone generation circuit 113 for generating dial key corresponding DTMF tone, for increasing the kind of tones. Here, the tone output time range in respect to a PCM highway L1 being limited by a main CPU 112, the main CPU 112 will be loaded heavily.
For example, an MF tone output from the MF tone generation circuit 114 will be arranged to the channel 0 (CH0) to the channel 31 (CH31) as shown in (21A) of FIG. 21, to be transmitted as input stream for MF tone. There, the time switch 111 outputs to the channel 2 and thereafter in the PCM highway L1 having channel 0 (CH0) to channel 31 (CR31), and this stream is shown by (21B) of FIG. 21. Here, the digit output time interval of MF tone is defined to 60 mS.+-.0.5 mS, so it becomes difficult to control the time interval when the main CPU 112 is loaded heavily.
Moreover, the PBX 10 will includes a MF signal source in addition to the MF signal source provided in the E911 unit 4; as a consequence, it will be redundant to have double MF signal source in a system. On the other hand, as the E911 unit 4 is connected to the PBX 10 outside, when E911 call can not originated through the E911 unit 4, it is necessary to verify whether the fault is due to the E911 unit 4 to network side, or to the general purpose bus 6, or to the PBX 10, increasing the time and work for restoration. Technology concerning such emergency call is disclosed in U.S. Pat. No. 5,235,630 or Japanese Patent Application 6-168318 (Publication No. 8-32703).